Nicene and Post-Nicene Fathers, Vol. V:A Work on the Proceedings of Pelagius.: Chapter 12

It was further objected against Pelagius, as if he had written in his book, that “evil does not enter our thoughts.” In reply, however, to this charge, he said: “We made no such statement. What we did say was, that the Christian ought to be careful not to have evil thoughts.” Of this, as it became them, the bishops approved. For who can doubt that evil ought not to be thought of? And, indeed, if what he said in his book about “evil not being thought” runs in this form, “neither is evil to be thought of,” the ordinary meaning of such words is “that evil ought not even to be thought of.” Now if any person denies this, what else does he in fact say, than that evil ought to be thought of? And if this were true, it could not be said in praise of love that “it thinketh no evil!” 1641
But after all, the phrase about “not entering into the thoughts” of righteous and holy men is not quite a commendable one, for this reason, that what enters the mind is commonly called a thought, even when assent to it does not follow. The thought, however, which contracts blame, and is justly forbidden, is never unaccompanied with assent. Possibly those men had an incorrect copy of Pelagius writings, who thought it proper to object to him that he had used the words: “Evil does not enter into our thoughts;” that is, that whatever is evil never enters into the thoughts of righteous and holy men. Which is, of course, a very absurd statement. For whenever we censure evil things, we cannot enunciate them in words, unless they have been thought. But, as we said before, that is termed a culpable thought of evil which carries with it assent.